Elastomer coated layer for erosion and/or fire protection

ABSTRACT

A method for preparing an uncured supported elastomer material includes the steps of: providing a fibrous reinforcement material; providing a layer of uncured elastomer material substantially adjacent to the fibrous reinforcement material; exposing the layer and the fibrous reinforcement to a temperature below a curing temperature and above a flow point of the uncured elastomer material, and a pressure sufficient that the uncured elastomer material flows into the fibrous reinforcement material, so as to provide an uncured supported elastomer material.

This is a Division, of application Ser. No. 08/645,669, filed May 14,1996.

BACKGROUND OF THE INVENTION

The invention relates to a supported elastomer material for use inproviding structures with enhanced erosion and/or fire resistance, to amethod for preparing such uncured supported elastomer materials, and toa method for reinforcing a structure with such a material. The presentinvention has particular utility in reinforcing various aerospacecomponents and the like, especially those having complex surfaces.

Composite and metallic aerospace components such as helicopter rotors,propellers, gas turbine engine fan blades, compressor airfoils, fan exitguide vanes, struts, nacelle gas path components and the like areexpected to operate under a wide variety of environmental conditions.Typically, these components are exposed to impingement from highrelative velocity particulate matter which causes the components todeteriorate. Further, extreme temperatures are frequently encountered.

Elastomer materials such as Viton™ have been studied and have been shownto provide effective erosion protection for composites or metals. Sheetsof elastomer such as Viton have been used by directly applying thissheet to simple surfaces such as nosecone caps for gas turbine enginesto provide effective erosion protection to same. The use of elastomersheet in these instances is successful because the surface geometry ofthe component is very gentle, and an elastomer sheet can therefore beapplied without significant wrinkling problems.

However, numerous components require enhanced erosion protection whereinthe components do not have simple or gentle surface geometry. Examplesof such components include helicopter rotors, propellers, gas turbineengine fan blades, compressor airfoils, fan exit guide vanes, struts,nacelle gas path components and the like. A recurring problemencountered during the application of sheets of elastomer to complexsurfaces is the formation of wrinkles in the elastomer sheet material.Another problem frequently encountered during the application ofelastomer sheet to complex surfaces are deep impressions caused forexample by underlying carbon fabric ply. Such wrinkling and impressionslead to relatively large numbers of unacceptable parts, therebyincreasing the overall cost of successfully fabricating reinforcedaerospace components having complex surfaces. In addition, extremethickness variations can result in the elastomer layer duringfabrication leaving some areas inadequately protected.

It is clear that the need exists for a reinforcement material for use inreinforcing components having complex surfaces which addresses theforegoing problems.

SUMMARY OF THE INVENTION

It is therefore the primary object of the present invention to provide amethod for preparing a reinforcement material for providing enhancedresistance to erosion.

It is a further object of the present invention to provide a method forpreparing a reinforcement material which is readily applicable tocomplex surfaces without wrinkling and impression.

It is still another object of the present invention to provide a methodfor preparing a reinforcement material.

It is a further object of the present invention to provide a method forreinforcing a component having a complex surface.

Still other objects and advantages of the present invention will becomemore apparent from the following description and drawings.

The foregoing objects are attained according to the invention by amethod for preparing an uncured supported elastomer material, whichmethod comprises the steps of providing a sheet of uncured elastomermaterial, providing a fibrous reinforcement material substantiallyadjacent to said sheet of uncured elastomer material, exposing saidsheet and said fibrous reinforcement to a temperature below a curingtemperature and above a flow point of said sheet of uncured elastomermaterial, and a pressure sufficient that said uncured elastomer materialflows into said fibrous reinforcement material, so as to provide saiduncured supported elastomer material.

In further accordance with the invention, a composite erosion resistantmaterial is provided which comprises a fibrous reinforcement layer and asheet of uncured elastomer material applied to and supported on saidfibrous reinforcement material.

Still further in accordance with the invention, a method is provided forreinforcing a part having a complex surface, which method comprises thesteps of providing an uncured supported elastomer material comprising afibrous reinforcement material and a layer of uncured elastomer materialsupported on and infused into said fibrous reinforcement material,providing a part having a complex surface to be reinforced, applyingsaid uncured supported elastomer material to said complex surface, andcuring said uncured supported elastomer material.

Other details and features of the process and material of the presentinvention are set out in the following description and drawings whereinlike reference numerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side schematic view of a portion of an erosion resistantmaterial in accordance with the invention;

FIG. 2 is an enlarged portion of the erosion resistant material of FIG.1;

FIG. 3 is a side schematic view of a portion of an erosion resistantmaterial according to an alternate embodiment of the invention; and

FIG. 4 is a side schematic view of a portion of an erosion resistantmaterial according to an alternate embodiment of the invention.

DETAILED DESCRIPTION

The invention relates to an erosion resistant material, a method forpreparing an erosion resistant material, and a method for reinforcing acomponent with an erosion resistant material, wherein the erosionresistant material is particularly effective at enhancing the erosionand/or fire resistance particularly of aerospace components havingcomplex surfaces such as helicopter rotors, propellers, gas turbineengine fan blades, compressor airfoils, fan exit guide vanes, nacellegas path components and the like, without excessive wrinkling,impressions or thickness variations of the resistant material.

Referring now to the drawings, FIG. 1 schematically illustrates aportion of an erosion resistant material 10 according to the invention.As shown, material 10 includes an elastomer material layer 12 and asubstantially fibrous reinforcement material layer 14 combined togetherso as to provide uncured elastomer material 12 supported onreinforcement material 14.

In accordance with the invention, material 10 can be prepared byproviding a quantity of uncured elastomer material, for example in sheetor layer form, and providing a quantity of fibrous reinforcementmaterial, contacting the elastomer material and fibrous reinforcementmaterial, and heating the contacted materials to a temperature above theflow point of the elastomer material and less than the curingtemperature of the elastomer material, under a pressure sufficient thatthe heated uncured elastomer material flows into the fibrousreinforcement material whereby the uncured elastomer material and thefibrous reinforcement material are effectively combined, preferably withthe uncured elastomer material at least partially infused into thefibrous reinforcement material.

In accordance with the invention, it is critical to keep the temperatureto which the elastomer and fibrous materials are exposed at a levelbelow the curing temperature of the elastomer material. Advantageously,this results in a final erosion resistant material product having anuncured elastomer material layer supported on a fibrous reinforcementlayer which can be applied to complex surfaces for reinforcement of samewherein the erosion resistant material is less subject to undesirablewrinkling, impressions and the like.

In accordance with the invention, suitable uncured elastomer materialmay be selected from the group consisting of fluoroelastomers such as,for example, Viton™ or Fluorel™; perfluoroelastomers such as Kalrez™;fluorosilicones such as AMS 7273; silicones and polyurethanes. Aparticularly preferred elastomer is Viton™ fluoroelastomer which hasbeen found to provide excellent erosion and fire resistance.

In accordance with the invention, elastomer material for use inpreparation of the erosion resistant material of the present inventionmay be provided through a number of different procedures. For example,elastomer material may be provided in layer form by calendaring from anelastomer gum-stock, elastomer material may be provided as an elastomersheet of the proper desired size, or elastomer material may suitably beprovided through spray coating or solution coating directly upon thereinforcement material. Calendaring of elastomer may preferably beperformed directly onto a fibrous reinforcement material in accordancewith the invention. Each of the foregoing methods of providing thedesired elastomer material may suitably be used in accordance with theinvention depending upon the particulars of the reinforcementpreparation and application procedures. Of course, other methods ofproviding suitable layers or sheets of elastomer material may be used inaccordance with the invention.

Suitable reinforcement materials in accordance with the inventioninclude continuous or discontinuous fibers or fabric of carbon, glass,alumina borosilicate such as Nextel™, nylon, metallic wire, metallicparticulate, aramid fiber or fabric such as Kevlar™, polybenzoxazole,polyester, Nicalon™ and graphite.

As set forth above, one form of the erosion resistant material of thepresent invention is prepared by applying the uncured elastomer materialto the fibrous reinforcement material at sufficient temperature and/orpressure that the uncured elastomer material remains uncured, butsoftens to the point where the elastomer material can flow, and thepressure is preferably sufficient during this treatment to drive flow ofuncured elastomer material into the fibrous reinforcement material so asto advantageously result in infusion of the elastomer material into thefibrous reinforcement so as to provide a firm support of elastomermaterial on the fibrous reinforcement. In accordance with the invention,the treatment temperature is preferably between about 75° F. to about500° F. When the elastomer material is Viton, a temperature of about200° F. has been found to be particularly well suited to inducing flowof the Viton fluoroelastomer material without curing same. The treatmentpressure sufficient to induce suitable flow and bonding is preferablybetween about 0 to about 1,000 psi. When the elastomer material isViton™ fluoroelastomer, and the temperature is about 200° F., atreatment pressure of about 45 psi has been found to be particularlysuitable.

Referring to FIG. 2, the treatment processes of the present inventionadvantageously result in flow or infusion of softened elastomer material12 across the original material interface 16 between elastomer materiallayer 12 and fibrous reinforcement material layer 14, so as to provideelastomer material 12 between and encompassing fibers of fibrousreinforcement material 14 thereby providing an effective intimatecontact between the fibrous reinforcement material 14 and the uncuredelastomer material 12 supported thereon.

In further accordance with the invention, the thickness of sheets orlayers of elastomer material 12 and reinforcement material 14 maysuitably be selected to provide the desired resistance and protectiondepending upon the conditions to which erosion resistant material 10 isto be exposed. Typically, however, a sheet or layer of uncured elastomermaterial 12 preferably has a thickness of between about 0.005 inches toabout 0.050 inches, while the reinforcement material may be provided asa sheet of material having a thickness of between about 0.002 inches toabout 0.040 inches.

It should be noted that erosion resistant material 10 in accordance withthe invention may suitably be provided with an elastomer material layer12 on either or both sides of fibrous reinforcement material 14. FIGS. 1and 2 illustrate fibrous reinforcement material 14 having a layer ofelastomer material 12 on one side only. In this embodiment, the erosionresistant material 10 according to the invention would be applied to thepart to be reinforced with elastomer material layer 12 facing outwardlyaway from the part.

FIG. 3 illustrates a resistant material 10 according to the inventionhaving elastomer material 12 supported on both sides of fibrousreinforcement material 14. In this embodiment, elastomer material 12 mayserve to enhance bonding of erosion resistant material 10 to the part tobe reinforced, and may also serve to provide additional dampening of theimpact of particulate matter and other erosion causing forces uponerosion resistant material 10 and the underlying component to beprotected.

Referring now to FIG. 4, in accordance with an alternative embodiment ofthe invention, pressure and temperature may be applied to elastomermaterial 12 and reinforcement material 14 so as to completely infuseelastomer material 12 into reinforcement material 14 as shown. This maybe desirable in accordance with the invention so as to further enhancethe support of elastomer material 12 on reinforcement material 14, andfurther so that elastomer material 12 is exposed at a bottom surface 18of erosion resistant material 10 so as to enhance the bonding ofresistant material 10 to a component as desired.

As set forth above, the erosion resistant material 10 of the presentinvention is particularly well suited to application to componentshaving a complex surface. In accordance with the invention, erosionresistant material 10 may suitably be applied to a complex surface, withor without adhesive, and may then be cured, after application, so as toprovide the complex surface with a reinforcement layer of erosionresistant material 10 according to the invention wherein problems suchas wrinkling and impressions are greatly reduced or eliminated.

In accordance with the invention, erosion resistant material 10 may beapplied to complex surfaces of parts to be reinforced through a numberof different methods including but not limited to resin transfer molding(RTM), compression molding, adhesive or other bonding, autoclave bondingand the like. Depending upon the application process to be used, curingof the uncured elastomer material may be accomplished during and/orafter the bonding step.

EXAMPLE 1

This example illustrates the advantages of preparation of the uncuredsupported elastomer material in accordance with the present invention.In this example, various samples of uncured Viton sheet having athickness of 0.010 inches are applied to a 0.004 inch 120 style wovenfiberglass fabric. In an air circulation oven having a cycle of 15minutes, the temperature was set to 200° F. at atmospheric pressure. Asample of Viton sheet was contacted with a sample of the wovenfiberglass fabric, and placed in the air circulation oven. The resultwas a softening of the still uncured Viton material, but without bondingor adhesion of the Viton to the fiberglass fabric.

A second sample was prepared identical to the first sample and placed inan autoclave under a nylon vacuum bag at 200° F. under a pressure of 45psi for 15 minutes. This time, the Viton layer softened and flowed verywell into the fabric, resulting in a composite material having theuncured Viton material supported on the fiberglass fabric.

Additional samples were prepared wherein Viton was successfully appliedto other reinforcement materials including nylon fabric, carbon uniweavefabric, carbon plain weave fabric and fiberglass scrim.

EXAMPLE 2

In this example, an erosion resistant material in accordance with thepresent invention was successfully applied to a test panel. An uncuredsupported Viton supported on fiberglass as prepared in Example 1 wasapplied on one side of a test panel comprising a stack of ten 6 inchsquares of carbon/epoxy prepreg, and the stack was placed on a caulplate. The uncured supported Viton was applied to the test panel withthe Viton layer facing the outside. The panel with Viton was bagged andcured in an autoclave according to existing 350° F. cure parameters.After the cure, the panel was cut for microstructural evaluation. Thebond lines between the carbon and glass, and glass and Viton, wereexamined and no anomalies were observed. Further, a standard test wasperformed to evaluate peel strength as between the supported Viton andunderlying test panel. The peel strength exhibited was adequate andequivalent to similar tests using unsupported Viton sheet. The uncuredsupported Viton according to the invention was also tested for erosionprotection and was found to provide equivalent protection as compared tounsupported Viton.

EXAMPLE 3

This example illustrates the advantages of supported uncured elastomerin accordance with the invention for reinforcement of components havingcomplex surfaces as compared to unsupported elastomer sheet material.The component to be reinforced was a composite fan exit case consistingof an inner ring, an outer ring, and ten 4-strut packs or 4-packs. The4-packs are fabricated using resin transfer molding. These struts arevulnerable to erosion and erosion protection for the struts is thereforedesirable. Sheets of unsupported uncured Viton were attempted to beapplied to the 4-packs, but problems were encountered including extremewrinkling and deep impressions from the underlying carbon fabric ply.These defects in actual production would result in rejection of theparts.

An erosion resistant material in accordance with the invention was thenprepared, consisting of uncured Viton sheet supported on 0.004 inch 108style fiberglass. The application of this material to the 4-packsresulted in significantly diminished wrinkling and no impressions. Thus,the erosion resistant material of the present invention exhibitsadvantageous characteristics especially for application to parts havingcomplex surfaces.

It is apparent that there has been provided in accordance with theinvention an erosion resistant material and method for preparing such anerosion resistant material which fully satisfies the objects, means andadvantages set forth hereinbefore. While the invention has beendescribed in combination with specific embodiments thereof, it isevident that many alternatives, modifications, and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andbroad scope of the appended claims.

What is claimed is:
 1. A composite reinforcement material forreinforcing a part having a complex surface, comprising:a fibrousreinforcement material; and a layer of uncured elastomer materialsupported on and infused into said fibrous reinforcement material so asto provide an uncured supported elastomer material between andencompassing said fibrous reinforcement material thereby providing aneffective intimate contact between the fibrous reinforcement materialand the uncured elastomeric material supported thereon.
 2. A compositematerial according to claim 1, wherein said uncured elastomer isselected from the group consisting of fluoroelastomers,perfluoroelastomers, fluorosilicones, silicones and polyurethanes.
 3. Acomposite material according to claim 1, wherein said reinforcementlayer is selected from the group consisting of carbon, glass, aluminaborosilicate, nylon, metallic wire, metallic particulate, aramid,polybenzoxazole, polyester, and graphite.
 4. A composite materialaccording to claim 1, wherein said layer of uncured elastomer materialhas a thickness of between about 0.005 inches to about 0.050 inches. 5.A composite material according to claim 1, wherein said reinforcementmaterial is a layer of material having a thickness of between about0.002 inches to about 0.040 inches.
 6. A composite material according toclaim 1, wherein said reinforcement material comprises a woven fabrichaving fibers with spaces therebetween, and wherein said layer ofuncured elastomer material extends into said woven fabric into saidspaces whereby said layer of uncured elastomer material is firmlysupported on said reinforcement material.